It's so easy to get things to 68°F it's not even funny. If you are souping when the chemicals are below 68, you set them in a warm water bath. If they're too warm, you set them in a cool water bath.

You can make warm water by turning on the warm water tap on your faucet. If you need to cool things down, you put a jug or two of water into the refrigerator, or use some ice from the freezer.

Predictable results require consistent procedures. Shoot identical film frames shot under identical conditions using identical settings. Developing one at 64° for 13:00 will result in a different image than developing the other at 75° for 9:00. This is due to the logarithmic (non-linear) nature of developing. Highlights do not develop at the same rate as shadows.

Looking for simple, cheap(relatively), effective means of having a constant temperature water supply to develop my black and white photos. I've looked at commercial units that are way above what I can pay.
Any sources for constant water temperature supply devices, especially used, would be great.
Thanks,
Gail

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Gail - Are you developing films or prints? If films, just use a kettle and a thermometer and mix up a jug of suitably warm water (eg 20 or 21C) for the developer and don’t worry about the temperature of the stop and fix baths. If doing prints, go to your local pet shop and buy a mains-electric plastic heating mat (looks like a thin square sheet of hard plastic) designed for reptiles to rest on. It’s essentially waterproof. Take it home and insert it into a protective plastic bag to keep it nice and clean, and then plug it in and leave it sitting under the middle of your developer tray. In cold weather it will bring your developer to about 23.5C, a good warm temperature for active development. Very safe, uses hardly any power, just turn it on and forget about it while you’re printing. Your print developer really needs to be above 20c if it’s going to do its thing - Andrew Wittner

Ive been running a bunch of rolls recently and focusing on temp (for no apparent reason) heres what I have found. For the record I am using a Paterson System 4 tank that holds 1 120 spool or 2 35mm spools. The thing to consider is the ambient room temperature.

In the colder months I have no problem keeping my apartment at 68 Degrees and thus just processing at room temp. I use distilled water so I let the gallon jugs sit for a while before processing always on the mark.

The bigger issue is in the warmer months in which case I need to cool the developer down a bit. Ambient temp is anywhere from 74-78 degrees depending on when I get home and turn my AC on. I mix up the dev in the measuring cup and then sit it in an ice bath to cool down to 68. Stir frequently to ensure even cooling. Once at 68 dump in and begin processing. Frankly for the ~10 minute process time I have not seen huge temperature rises on the last 4 rolls I did yesterday. Water has a fairly high specific heat and will hold temp well over a short time span. The paterson tank allows you to insert a thermometer so I keep an eye on it in between agitations and submerge in the ice bath if the temperature is rising too much.

If you are using ilford film and developers they provide very accurate correction charts for processing at a range of temperatures. I have used these with great success. You can find it all on their website but you will need to download the data sheets for the individual film stocks.